Chemoenzymatic synthesis of a sialylated diantennary N-glycan linked to asparagine

Article abstract of DOI:10.1016/S0008-6215(97)10056-8

A partial structure of many glycoproteins, a glycosylated asparagine carrying a complex type undecasaccharide N-glycan (Neu5Ac(α2-6)Gal(β1- 4)GlcNAc(β1-2)Manαl3)[Neu5Ac(α2-6)Gal(β1-4)GlcNAc(β1-2)Man(α1- 6)]Man(β1-4)GlcNAc(β1-4)GlcNAcAsn) was obtained by total synthesis. As a starting material served a chemically synthesized diantennary heptasaccharide azide which was deprotected in a three-step sequence in high yield. The reduction of the anomeric azide was accomplished with propanedithiol in methanol-ethyldiisopropylamine. Coupling of the glycosyl amine to an activated aspartic acid gave the benzyl protected asparagine conjugate. After removal of the six benzyl functions the resulting free heptasaccharide asparagine was elongated enzymatically in the oligosaccharide part. The use of β-1,4-galactosyltransferase and α-2,6-sialyltransferase in the presence of alkaline phosphatase allowed the efficient transfer of four sugar units to the acceptor resulting in a full length N-glycan, a sialylated diantennary undecasaccharide-asparagine of the complex type.